首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   78867篇
  免费   4263篇
  国内免费   88篇
林业   3185篇
农学   2045篇
基础科学   462篇
  8570篇
综合类   15398篇
农作物   3127篇
水产渔业   3417篇
畜牧兽医   41722篇
园艺   844篇
植物保护   4448篇
  2019年   720篇
  2018年   1091篇
  2017年   1213篇
  2016年   1047篇
  2015年   903篇
  2014年   1189篇
  2013年   2623篇
  2012年   2111篇
  2011年   2573篇
  2010年   1614篇
  2009年   1729篇
  2008年   2594篇
  2007年   2403篇
  2006年   2285篇
  2005年   2138篇
  2004年   2074篇
  2003年   2134篇
  2002年   1921篇
  2001年   2384篇
  2000年   2438篇
  1999年   1869篇
  1998年   720篇
  1997年   711篇
  1996年   712篇
  1995年   806篇
  1993年   740篇
  1992年   1554篇
  1991年   1750篇
  1990年   1635篇
  1989年   1646篇
  1988年   1472篇
  1987年   1534篇
  1986年   1597篇
  1985年   1547篇
  1984年   1184篇
  1983年   1057篇
  1982年   704篇
  1979年   1152篇
  1978年   894篇
  1977年   755篇
  1975年   774篇
  1974年   1024篇
  1973年   1024篇
  1972年   1043篇
  1971年   993篇
  1970年   987篇
  1969年   903篇
  1968年   810篇
  1967年   799篇
  1966年   732篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
161.
OBJECTIVE: To develop and assess the reproducibility of a protocol to noninvasively test endothelial function in dogs on the basis of the flow-mediated vasodilation (FMD) procedure used in humans. ANIMALS: 5 healthy spayed female dogs. PROCEDURES: Luminal arterial diameter and blood flow velocity in the brachial and femoral arteries were measured with ultrasonography. The within-dog reproducibility of these ultrasonographic measurements was tested. An occlusion period of 1, 3, or 5 minutes with an inflatable cuff was used to create the FMD response. Measurements made at 15, 30, and 60 seconds following release of the occlusion were compared with measurements made immediately prior to each occlusion to assess the FMD response. RESULTS: Within-dog reproducibility of measurements revealed moderate to high correlations. Change from baseline in luminal arterial diameter was most substantial when measured at 30 seconds following release of occlusion, whereas blood flow velocity changes were maximal when measured at 15 seconds following release. The brachial imaging site provided a larger number of significant FMD responses than the femoral site. The 3-minute occlusion period provided equal or better responses than the 5-minute occlusion period. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasonographic measurement of the FMD responses was a feasible and reproducible technique and significant changes from baseline were detected. The FMD responses in dogs were most substantial when performed at the brachial artery with blood flow velocity and luminal arterial diameter changes from baseline measured at 15 and 30 seconds, respectively, following release of a 3-minute occlusion period.  相似文献   
162.
OBJECTIVE: To evaluate the effects of a weight reduction program combined with a basic or more complex physical therapy program including transcutaneous electric nerve stimulation on lameness in overweight dogs with osteoarthritis. DESIGN: Nonblinded prospective randomized clinical trial. Animals-29 adult overweight or obese dogs with a body condition score of 4/5 or 5/5 and clinical and radiographic signs of osteoarthritis. PROCEDURES: A weight-loss program was initiated for all dogs. One group received caloric restriction and a home-based physical therapy program. The other group received the identical dietetic protocol and an intensive physical therapy program including transcutaneous electrical nerve stimulation. Lameness was assessed clinically and by kinetic gait analysis on a treadmill with 4 force plates to measure symmetry of ground reaction forces (GRFs) of the affected and contralateral limbs in bimonthly intervals for 6 months. RESULTS: Significant weight loss was achieved in both groups; however, greater weight reduction was attained by dogs treated with caloric restriction and intensive physiotherapy. Mobility and symmetry indices of GRFs were improved after 6 months; the best outcome was detected in the group receiving energy restriction combined with intensive physical therapy. CONCLUSIONS AND CLINICAL RELEVANCE: Caloric restriction combined with intensive physical therapy improved mobility and facilitated weight loss in overweight dogs. The combination of dietetic and physical therapy may help to improve the health status more efficiently than dietetic treatment alone.  相似文献   
163.
164.
165.
The pathologic features of a nasal chondrosarcoma, a rare tumor of bovines, in a Simmental cow are described. Upon clinical examination, stertor, difficulty in breathing, poor body condition, and a nasal mass were found. Histopathologic examination revealed that the mass was composed mostly of numerous cartilaginous lobules surrounded by spindle-shaped cells, often showing mitotic figures, atypical chondrocytes, and lacunae containing 2 or more cells. On the basis of the histological features, the mass was diagnosed as a nasal chondrosarcoma.  相似文献   
166.
167.
168.
The use of topical pharmaceutical formulations is increasingly popular in veterinary medicine. A potential concern is that not all formulations are registered for the intended species, yet current knowledge strongly suggests that simple extrapolation of transdermal drug pharmacokinetics and pharmacodynamics between species, including humans, cannot be done. In this review, an overview is provided of the underlying basic principles determining the movement of topically applied molecules into and through the skin. Various factors that may affect transdermal drug penetration between species, between individuals of a particular species and regional differences in an individual are also discussed. A good understanding of the basic principles of transdermal drug delivery is critical to avoid adverse effects or lack of efficacy when applying topical formulations in veterinary medicine.  相似文献   
169.
Feeding obese dogs a high-fiber food with or without added conjugated linoleic acid (CLA) resulted in reduced caloric consumption, reduced body weight, and a 3.3% reduction in body fat, whereas feeding a low-fiber food resulted in a comparable increase in caloric consumption and a 2.4% gain in body fat. The addition of CLA did not significantly affect food intake, energy intake, final lean body percent, change in lean body percent, or final fat percent. These results suggest that the addition of dietary fiber but not CLA to foods may be helpful in the treatment of canine obesity.  相似文献   
170.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号